Ninjurin-1 (nerve injury-induced protein 1) is a 20-22 kDa member of the Ninjurin family of transmembrane (TM) proteins. It is expressed by Schwann cells, neurons and hepatocytes and participates in intercellular homophilic binding during nerve regeneration. Human Ninjurin-1 is 152 amino acids in length. It has an unusual membrane orientation. There is an 80 amino acid (aa) N-terminal extracellular domain (ECD) (aa 1-80), followed by a TM segment, a cytoplasmic region, a second TM segment and a C-terminal ECD (aa 142-152). Homophilic binding is divalent-cation dependent and occurs between Pro26 and Asn37. Over aa 1-80, human Ninjurin-1 shares 84 percent aa sequence identity with mouse Ninjurin-1. Human Ninjurin-1 shares only 50 percent aa sequence identity with human Ninjurin-2.